Answers

I haven’t been able to find any specific information on how long corks will last submerged in water, but my guess is that they will last a very long time. If the bottle has air in it it won’t sink and the cork probably won’t be submerged anyway.

However, since this is an environmental website, I think I should advise you to pick a different kind of time capsule that doesn’t involve throwing a bottle into a lake. Try burying the bottle in a spot you mark so you can be sure to find it again, or even just putting a box in the attic.